Many types of implantable medical devices (IMDs) have been clinically implanted over the last twenty years that deliver relatively high-energy cardioversion and/or defibrillation shocks to a patient's heart when a malignant tachyarrhythmia, e.g., atrial or ventricular fibrillation, is detected. Cardioversion shocks are typically delivered in synchrony with a detected R-wave when fibrillation detection criteria are met, whereas defibrillation shocks are typically delivered when fibrillation criteria are met and an R-wave cannot be discerned from the EGM.
Current implantable cardioverter/defibrillators (ICDs) or implantable pacemaker/cardioverter/defibrillators (PCDs) include programmable parameters such as multiple arrhythmia detection criteria/levels, multiple therapy prescriptions (e.g., stimulation at pacing levels (atrial/ventricular/dual chamber atrial & ventricular for bradycardia, bi-atrial and/or bi-ventricular for heart failure patients and arrhythmia overdrive or entrainment stimulation) and high level stimulation via cardioversion and/or defibrillation), extensive diagnostic capabilities and high speed telemetry systems. These ICDs or PCDs are typically implanted into patients who have experienced a significant cardiac event.
Attempts at identifying those patients who are asymptomatic by conventional measures but are nevertheless at risk of a future sudden death episode are being undertaken. Current studies of patient populations, e.g., the MADIT II and SCDHeFT studies, are establishing that there are large numbers of patients in any given population that are susceptible to sudden cardiac death, and that they can be identified with some degree of certainty. One option proposed for this patient population is to implant a prophylactic subcutaneous implantable cardioverter/defibrillator (SubQ ICD) to deliver therapy in the event of a cardiac episode, such as sudden cardiac arrest, in order to reduce the risk of death resulting from the episode, and who will then have a full-featured ICD with transvenous leads implanted.
Current implanted subcutaneous coil leads are complicated and time consuming to implant and may dislodge or pull back acutely. Further, fibrosis and tissue build-up make it impossible to remove intracardial leads after a few month of implant.
Therefore, for these and other reasons, a need exists for an improved method and apparatus for a subcutaneously implanted lead that is easy to implant and stays fixed in the proper location acutely and chronically, or until it becomes desirable to remove the lead for repositioning or remove the lead permanently.